The invention relates to a photocell based on gallium arsenide or indium phosphide.
Peak efficiency factors of about 20 % are achieved with solar cells made of the most widely used material, crystalline silicon. With gallium arsenide, higher efficiency factors are possible, namely up to 26 %. The higher efficiency in the case of gallium arsenide is due to a higher energy band gap of 16 eV, or a better adaptation to the spectral distribution of sunlight (c.f.: Siemens Energietechnik [Siemens Power Engineering), 2nd issue (1980), pp. 266-269). However, producing these types of photocells entails the following problems which need to be solved:
protecting the surface of the semiconductor structure from chemical influences and mechanical effects, in other words passivation; PA1 elimination of surface reflections; PA1 producing a space-charge region for charge-carrier separation (p-n junction or Schottky barrier).
Photocells based on gallium arsenide or indium phosphide require extensive doping of the semiconductor to produce the p-n junctions. From a technical standpoint, this is very costly and involves many risks (i.e., insulation failures). Schottky barriers, which are produced as a result of the metal/semiconductor contact, absorb incident light or have too high of a resistance. According to the present state of the art, the passivation of these types of photocells is accomplished with the help of plastic layers, however the layers' moisture-blocking capability is limited. Passivation of these photocells can also be accomplished with glass, in which case, however, bonding is required.